A power supply device, which uses a device used at a power plant or the like (an electromagnetic valve, a motor, or the like) as a load and supplies power to the load, (for example, a current output circuit for setting current, which flows in the load, to a prescribed value) is subjected to soundness diagnosis for the improvement of reliability thereof.
As a method of diagnosing soundness, for example, PTL 1 discloses a method including: a step of directly connecting means for generating an AC voltage including a rectangular pulse to the primary side of a transformer or connecting the means to the primary side of the transformer through a rectifying circuit; a step of directly connecting a drive target, which is to be subjected to any one of measurement, drive, and control, to the secondary side of the transformer or connecting the drive target to the secondary side of the transformer through a rectifying circuit; a step of measuring the change of primary-side current, which is caused by current consumption caused by the operation of the drive target connected to the secondary side, by power supplied through the transformer; and a step of diagnosing an operation and a signal state of the drive target by a result of the measurement.
Further, multiple (for example, two) power supply means are provided in a power supply device, and power supply means that supplies power to a load is switched to the other power supply means when abnormality occurs in power supply means that supplies power to the load.